On the applicability of the surface equivalence theorem inside enclosures

A scenario of a generic printed circuit board (PCB) representing an electronic module inside a metallic enclosure is studied numerically. Following the surface equivalence theorem, the PCB is replaced with surface currents running on a Huygens box (HB) inside the enclosure and near-field errors with respect to the full model are observed. In concordance with previous work it is found that leaving the HB empty leads to significant errors. This time, however, countermeasures in the form of including the ground plane or substrate of the PCB inside the HB have the desired effect of reducing the errors at only some of the investigated frequencies.